What's a Hacker
The term "hacker" in modern usage is often used to refer to unauthorized intruders and attackers, people who gain access to others' systems for the purpose of causing damage, virus writers and the like. The word "hacker" originated at MIT, and when first applied to computer users, simply referred to someone who was a talented programmer, especially one with a natural affinity for computers (i.e. without formal training). You can find good discussion of the origin of the term "hacker" in the 1984 book Hackers: The Heroes of the Computer Revolution.
Within the hacker community, there is a division between those who are known as "black hat hackers" (the ones whose goals are to steal data, bring down networks, crash computers and otherwise cause problems) and "white hat hackers" who use their hacking skills for beneficial purposes, such as developing security programs to keep the black hats out. Many of the people creating chaos on networks today aren't really even hackers at all. Hackers of either variety by definition are skilled programmers. Many of the most destructive attackers and intruders are mere "script kiddies" - people who don't have the ability to create attacks or gain access themselves, but use programs written by someone else to do it. It's a shame that a word that once was a badge of one's talent and knowledge has become a synonym for "criminal" due to the actions of some.